This invention relates to the decontamination of fluids, surfaces and objects, and more specifically to the use of an energy source for the decontamination of fluids, surfaces and objects contaminated with chemical or biological agents.
The use of a non-thermal plasma to destroy pollutants is known. A non-thermal plasma is a plasma in which electrons, rather than a gas, are excited. Ozone generators commonly use a non-thermal plasma to produce ozone. Devices that produce non-thermal plasmas are often referred to as corona discharge generators. These devices generally operate by using very short duration, high voltage pulses (pulsed corona discharge) applied to an electrode. A corona discharge generator that employs a dielectric coating on the electrode is sometimes referred to as a barrier or silent corona discharge device. Tesla coils are often used as the high voltage source for a pulsed corona discharge; however, the pulsed corona discharge produced by a Tesla coil is often quite loud.
Recently, non-thermal plasmas have been used to remove pollutants from gas streams. U.S. Pat. No. 4,954,320, xe2x80x9cReactive Bed Plasma Air Purification,xe2x80x9d describes one such use of a non-thermal or corona discharge device used to detoxify a gas stream by passing the gas stream through a non-thermal plasma. The reactive bed plasma device described therein produces an active plasma, which yields energetic free electrons and highly reactive chemical species, especially oxygen atoms, to promote rapid oxidative decomposition of the contaminants in the air stream. This oxidation is similar to the process of incineration with the most notable difference being the dramatically reduced operating temperatures of the reactive bed plasma device. Electron impact is the driving force of plasma-induced decomposition, because it creates more free electrons, ions, reactive neutrals, and radicals. Another result of direct energy input at the quantum level is the emission of ultraviolet light from nitrogen molecules in the surrounding air. This ultraviolet radiation is capable of breaking some chemical bonds, ionizing many compounds, and disinfecting selected biological contaminants upon prolonged exposure.
While the prior art seems to suggest that a non-thermal plasma may be useful for treating a stream of gas, there is much less teaching of how to apply a non-thermal plasma to the decontamination of a surface or an object. Experimental chambers have been constructed to batch treat small objects with a non-thermal plasma. While such chambers can be useful in treating small, easily handled objects, it would be desirable to develop a system that enables a non-thermal plasma to destroy contaminants on the surfaces of large objects. It would further be desirable to develop a decontamination system that can distribute a non-thermal plasma to a wide variety of contaminated materials, including surfaces, objects, and fluids. The prior art does not teach or suggest how such a distributed non-thermal plasma generator can be achieved to provide for the independent or simultaneous decontamination of surfaces, object, or fluids.
While generally planar surfaces can be decontaminated using a non-thermal plasma generator that does not exhibit much dimensional flexibility, the decontamination of an irregularly-shaped object having non-planar surfaces would require a non-thermal plasma generator sufficiently large and flexible enough to drape over the object, so that the non-thermal plasma can xe2x80x9cblanketxe2x80x9d the object to be treated. The prior art does not teach or suggest how such a dimensionally flexible non-thermal plasma generator can be achieved.
An additional drawback of prior art non-thermal plasma generators is their relatively high power requirements. While such power levels as required for prior art devices may be readily supplied for compact non-thermal plasma generators, substantially larger non-thermal plasma generators will require correspondingly greater levels of power. Thus, a relatively large non-thermal plasma generator could not be easily powered by a portable power source, such as a battery. It is desirable that a non-thermal plasma generator based decontamination system scaled up to a relatively large size (able to decontaminate an object the size of a vehicle, for example) should still require power levels providable by portable power supplies. It would be further desirable that smaller non-thermal plasma generator based decontamination systems be powered by small batteries, such that non-thermal plasma generator based decontamination systems can be incorporated into small products such as personal air purifying respirators (APRs). The prior art also does not teach or suggest such systems.
While the prior art teaches using a non-thermal plasma to destroy the pollutants in a gas stream, there exists a wide range of chemical and biological agents that can contaminate surfaces, objects, or fluids, the destruction of which is not discussed in the prior art. Releases of chemicals from farms, factories and homes can contaminate soils. Fungi and spores can contaminate seeds and foodstuffs, and even the soil used to grow crops. Disease causing microorganisms are frequently present on surfaces, objects, and within the air. Allergens and toxins are frequently present in the outside ambient air, as well as the air within buildings (i.e., the xe2x80x9csick building syndromexe2x80x9d).
Additionally, potential terrorist use of chemical and biological agents represents an ever-growing threat to populations and property. The release of the chemical warfare agent Sarin in the Tokyo subway system by the Aum Shinrikyo cult has drawn widespread attention to the potential use of chemical and biological agents in attacks by terrorist or dissident groups. Also of concern is the fact that use of chemical and biological warfare agents by foreign powers during military actions seems much more likely in view of events in the Middle East during the last decade. Military vehicles and other objects exposed to chemical and biological contamination represent a hazard if their surfaces are contacted by unprotected personnel. Decontamination of an area or object after the actual or suspected release of such agents thus poses significant challenges and risks.
It therefore would be desirable to develop a decontamination system that is effective against a wide range of biological and chemical agents, while minimizing incidental damage to the surface or object being decontaminated. It would further be desirable for such a decontamination system to have a low power requirement so that batteries or other readily portable power sources could be employed to energize the system. A desirable system of this type should operate at ambient pressure and temperature and should not consume large quantities of reagents nor produce large quantities of waste byproducts. A desirable decontamination system should be able to readily destroy contaminants disposed within cracks or crevices of a surface or object. Finally, such a system should be well adapted to decontaminating almost any fluid stream, such as breathing or medical air; as well as almost any surface, such as floors, desks, or walls, and more complex objects, such as irregularly-shaped tools, vehicles, and other equipment.
In accord with the present invention, apparatus are defined for detoxifying chemical or biological agents. These agents may be on a surface or entrained in a fluid. The distributed plasma reactor apparatus includes a non-thermal plasma generator, which when activated by a sufficiently high voltage, produces a plasma discharge. The plasma discharge is adapted to be positioned in proximity to the chemical or biological agents so that reactants produced by the plasma discharge detoxify the chemical or biological agents. A power source capable of energizing the non-thermal plasma generator at a high voltage is electrically coupled to the non-thermal plasma generator to activate it.
In one preferred embodiment, the distributed plasma reactor comprises a large surface of distributed electrodes, or xe2x80x9cplasma blanket,xe2x80x9d which is adapted to be disposed adjacent to a surface to be decontaminated, such that the plasma discharge is produced near the surface. Preferably, the plasma blanket is sufficiently flexible to drape over an irregularly-shaped object having non-planar surfaces that are to be decontaminated.
For portable applications, the power source comprises a battery and a high voltage inverter that converts a direct current produced by the battery to the high voltage used to activate the plasma generator.
In several embodiments, the distributed plasma reactor comprises a silent discharge type non-thermal plasma generator, while in other embodiments, the distributed plasma reactor comprises a pulse discharge type non-thermal plasma generator.
In the silent discharge type, the non-thermal plasma generator includes one or more dielectric covered electrodes and one or more bare electrode that are connected to the power source so that the high voltage is applied between the dielectric covered electrodes and the bare electrodes. In one embodiment, the bare electrode is formed in an accordion-folded pleated configuration and the dielectric covered electrodes pass through adjacent pleats of the bare electrode.
To decontaminate a larger area, the distributed plasma reactor includes a plurality of dielectric covered electrodes and may include a plurality of bare electrodes. In one preferred form, the bare electrode comprises a conductive mesh that is relatively flexible.
One embodiment of a plasma blanket includes a sheet of non-conductive material that is substantially parallel to the plurality of dielectric covered electrodes. This sheet serves to direct the plasma discharge onto the surface to be decontaminated.
In one preferred embodiment, the bare electrode is helically wrapped around the dielectric covered electrode. A plurality of bare and dielectric covered electrodes of this type can be attached to and supported by a flexible substrate.
The bare electrode can be formed as a sheet, which may comprise a metal foil, or a conductive mesh. The dielectric covered electrode preferably extends through the bare electrode. Two or more bare electrodes configured as sheets can be spaced apart from each other in parallel, to define a treatment volume through which a contaminated fluid is conveyed.
A plasma discharge is produced at each intersection where a bare electrode and a dielectric covered electrode overlap, intersect, or where the bare electrode is helically coiled about the dielectric covered electrode.
In another embodiment of the distributed plasma reactor, a dielectric covered electrode has a first end electrically coupled to the power source, and a non-thermal corona discharge is generated at a second opposite end of the dielectric covered electrode. Preferably, the dielectric covered electrode further comprises a multi-stranded conductor, and at the second end of the dielectric covered electrode, the conductor is separated into individual strands, such that a non-thermal corona discharge is generated by each individual strand. This embodiment is excited by a high frequency pulsed source.
In still another embodiment, the distributed plasma reactor comprises a non-conductive substrate supporting a plurality of spaced-apart point electrodes and a plurality of spaced-apart dielectric spacers. The plurality of electrodes and the plurality of dielectric spacers are connected to a surface of the non-conductive substrate and extend away from the surface. The dielectric spacers extend substantially farther from the surface than the point electrodes to maintain a space between the point electrodes and the surface to be decontaminated, preventing the point electrodes from shorting to ground on that surface.
Another aspect of the present invention is directed to a method for decontaminating a substance by destroying a toxic material that has contaminated the substance. The method includes the step providing a power source that produces a voltage sufficiently great to generate a plasma discharge. A distributed plasma reactor is positioned proximate to the substance that is to be decontaminated. The distributed plasma reactor is then activated with the power source, producing a non-thermal plasma discharge that destroys the toxic material, thereby decontaminating the substance. Other functional steps of the method are generally consistent with the description of the apparatus set forth above.